Novel anti-oxidant additive and oxidation resistant lubricant composition



United States Patent 3,095,378 NOVEL ANTI-QXIDANT ADDITIVE AND GXEDA- TION RESISTANT LUBRICANT COMPOSTTIUN Harold J. Watson, Danville, Va., assignor to Texaco Inc,

7 a corporation of Delaware NoDrawing. Filed June 18, 1958, Ser. No. 742,760 2 Claims. (Cl. 252-496) This invention relates to a novel compound and to a lubricant composition containing this novel compound having excellent resistance to oxidation. One of the problems in lubricating, particularly at high temperatures, is to develop lubricating compositions which will not easily oxidize to form acidic components which create harmful deposits or sludge in the composition. This problem is especially diflicult toovercome when dealing with extremely high temperatures encountered in modern gas turbine engines and hydraulic systems.

Many anti-oxidant additives for lubricating compositions have been developed to help the lubricant remain stable under oxidizing conditions. In particular, Patent No. 2,202,877, discloses anti-oxidants comprising trialkylated monohydroxy phenols represented by the following structural formula:

wherein R, R and R" represent alkyl groups and wherein at least one of the alkyl groups in a position ortho to the hydroxyl group contain 3 or more carbon atoms. The best antioxidant additive compound found which met the above description was 2,6-di-tertiary :butyl-4-methyl phenol. This compound has been extensively used commercially as an anti-oxidant additive for lubricating oil with excellent eiiect.

In accordance with the present invention, a superior anti-oxidant compound has been developed. This compound adheres to the following general formula:

wherein R and R are alkyl groups having from 1 to 5 carbon atoms, at least 1 of said alkyl groups having at least 3 carbon atoms. Examples of these compounds include:

2,6-di-tertiary butyl-4-(isopropoxymethyl) phenol 2,6-di-isopropyl-4-(isopropoxymethyl) phenol 2,6-di-secondary butyl-4-(isopropoxymethyl) phenol 2,6-di-secondary amyl-4-(isopropoxymethyl) phenol 2-secondary butyl-6-tertiary amyl-4-(isopropoxymethyl) phenol Z-tertiary butyl-6-isopropyl-4-(isopropoxymethyl) phenol 2-secondary butyl-6-tertiary butyl-4-(isopropoxymethyl) phenol 2,6-di-n-=butyl-4-(isopropoxymethyl) phenol 2,6-di-n-propyl-4-(isopropoxymethyl) phenol 2,6-di-n-amyl-4-(isopropoxyrnethyl) phenol 2-methyl-6-tertiary butyl-4-(isopropoxymethyl) phenol 2-tertiary butyl-6-ethyl-4-(isopropoxymethyl) phenol Of the above compounds, 2,6-di-tertiary butyl-4-(isopropoxymethyl) phenol is preferred.

The compounds of the invention are included in lubricating oils in antioxidant amounts to produce excellent lubricating compositions. Generally the amount ranges from 0.05 to 2 percent by weight based on the total lubricant composition. The preferred range is about 0.1 to 0.5 percent. The base oils with which these novel antioxidant additives are used are hydrocarbon lubricating oils, synthetic lubricating oils and mixtures thereof. The hydrocarbon oils include mineral, vegetable and animal oils but particularly hydrocarbon mineral oils which can be paraflin base, naphthene base, or residual type oils.

The synthetic lubricating base oils include high molecular weight polyalkylenes and high molecular weight, high boiling liquid aliphatic dicarboxylic acid esters which possess excellent viscosity-temperature relationships and lubricating properties, and are finding ever increasing utilization in lube oils and greases adapted for high and low temperature lubrication. Examples of the ester class of synthetic lubricating bases are the diesters of acids such as sebacic, adipic, azelaic, alkenyl succinic, etc.; specific examples of these diesters are di-Z-ethylhexyl sebacate, di-Z-ethylhexyl azelate, di-Z-ethylhexyl adipate, di-n-amyl sebacate, di-Z-ethylhexyl-n-dodecyl succinate, .di-Z-ethoxyethyl sebacate, di-2'-methoxy-2-ethoxyethyl sebacate (the methyl Carbitol diester), di-2'-ethyl-Z-n-butoxyethyl seba cate (the Z-ethylbutyl Cellosolve diester), di-2-n-butoxyethylazelate (the n-butyl Cellosolve diester) and di-2-nbutoxy-Z-ethoxyethyl-n-octyl succinate (the n-butyl Carbitol diester).

A preferred high molecular weight polyalkylene is the polybutene having a molecular weight range of from 500-1500.

Polyester lubricants formed by a reaction of an aliphatic dicarboxylic acid of the type described above, a glycol and a monofunctional aliphatic monohydroxy alcohol or an aliphatic monocarb-oxylic acid in specified mole ratios are also employed as the synthetic lubricating base in the compositions of this invention; polyesters of this type are described in US. 2,628,974 to Robert T. Sanderson, issued February 17, 1953. Polyesters formed by reaction of a mixture containing specified amounts of dipropylene glycol, sebacic acid and 2-ethylhexanol and of a mixture containing adipic acid, di-ethylene glycol and Z-ethylhexanoic acid illustrate this class of synthetic polyester lubricating bases.

Polyalkylene ethers as illustrated by polyglycols are also used as the lubricating base in the compositions of this invention. Polyethylene glycol, polypropylene glycol, polybutylene glycols and mixed polyethylene-polypropylene glycols are examples of this class of synthetic lubricating bases.

The sulfur analogs of the above-described diesters, polyesters and polyalkylene ethers are also used in the formulation of the lubricating compositions of this invention.

Dithioesters are exemplified by di-Z-ethylhexyl thiosebacate and di-n-octyl thioadipate; polyethylene thioglycol is an example of the sulfur analogs of the po-lyalkylene glycols; sulfur analogs of polyesters are exemplified by the reaction product of adipic' acid, thioglycol and 2-' ethylhexyl mercaptan.

The anti-oxidant additives in the present invention are particularly useful when incorporated in oils used in heavy, high speed turbine engines. These oils are broadly characterized as paraffin base and naphthene base oils having a viscosity range from 80 to 780 SSU at 100 F., a flash range of from 320 to 520 F., a pour range of from +20 to -45 F. and a viscosity index of 95 to less than 1().

Turbine oils, in addition to anti-oxidant additives, usually have anti-rust agents incorporated therein to inhibit rusting under the severe conditions to which the oils are subjected. Anti-rust compounds which may be advantageously mixed 'with turbine oils are broadly defined as aliphatic substituted aliphatic di-carboxylic acids. These anti-rust compounds can be used with or without minor portions of mono or diesters of inorganic acids or mixtures thereof, such as an admixture of mono and dilauryl phosphoric acid esters. For a further description of these anti-rust compounds see US. Patent 2,452,319 to John A. Patterson and Herman D. Kluge, issued October 26, 1948, and assigned to The Texas Company.

Other additives such as anti-foam agents can be advantageously incorporated in the lubricating oils of the invention. These anti-foam agents are usually silicones such as dimethyl silicone.

The novel compounds of this invention are prepared by treating 2,6-C -C alkyl-4-methy-l phenol with an equimolar amount of N-bromosuccinimide and then treating the product with an alkali metal isopropoxide. The following is an example of the preparation of 2,6-di-tertiary butyl-4-(isopropoxymethyl) phenol.

EXAMPLE I 22.0 g. of 2,6-di-t-butyl-4-methyl phenol were placed with 17.7 g. of N-b-romosuccinimide in a refluxing vessel containing 150 of carbon tetrachloride. The reaction mixture was refluxed for a period of 4 hours. The reaction product, 2,6-di-t butyl-4-bromomethyl phenol, was treated with a previously reacted 2.3 gms. of sodium in 200 ml. of isopropyl alcohol to form sodium isopropoxide. This was added dropwise to the carbon tetrachloride solution and reacted quickly therewith to form 2,6-di-t-butyl-4-(isopropoxymethyl) phenol. The above mixture was refluxed for 30 minutes. The product was purified by pouring the mixture into water acidifying with HCl until a water layer was acid to Congo red paper. The Water layer was extracted with ether and the ether extract added to the C01 layer which had been previously separated. This organic layer was stripped to 100 C./ 30 mm. The product was then distilled under vacuum, 3 cuts taken and cuts 2 and 3 dissolved in hot hexane and cooled to obtain leafy plates. The purified product had the following properties.

Boiling point, C 101-108/225 microns. Melting point, C 58.5-60.

Carbon, percent 77.8 (theor. 77.7). Hydrogen, percent 10.9 (theor. 10.8). Oxygen, percent 11.4 (theor. 11.5).

The value of the compound of this invention as an anti-oxidant in lubricating oils is demonstrated in the results of a turbine oil oxidation test (ASTM D94354) which are set forth in the following table. The base oil used in the ASTM. oxidation test was cut from an A grade naphthene base crude which was solvent refined, heavily acid treated, neutralized, steamed and brightened Table I ASTM OXIDATION TEST Base Oi1+0.3% (\vt.) Anti-oxidant Hours 2,6di-t-butyl-i-methyl phenol 1, GOO-1,500 2.6-di-t-butyb4-(methoxymethyl) phenol 1,000-1, 150 2,6-di-t-butyl4 (eth oxymethyl) phenol 1, 200-1, 400 2,6di-t-butyl-4(n-butoxymethyl) phenol 1,100-1 2,6-di-t-butyl-4(isopropoxymethyl) phenol- 1, 900-1, 900

The anti-oxidant additives of this invention as represented by 2,6-di-tertiary butyl-4-(isopropoxymethyl) phenol, show unexpectedly superior anti-oxidant properties in the base oil as compared to the best known prior art anti-oxidant, 2,6-di-tertiary 1butyl-4-methyl phenol running from 400 to 800 more hours under the severe oxidizing conditions of the test procedure before failure. It is also unexpectedly superior in lending oxidation stability to the base oil as compared to the closely related chemical compounds listed in Table I which were prepared in the same manner except that the sodium isopropoxide used in the preparation of the isopropoxymethyl phenol was replaced with methyl alcohol, ethyl alcohol and n-butyl alcohol respectively in the reactions.

Obviously, many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. A mineral lubricating oil containing an anti-oxidant amount of a compound having the following formula:

2. A mineral lubricating oil containing a rust-inhibiting amount of an oil soluble alkenyl succinic acid, a foam inhibiting amount of a dimethyl silicone and anti-oxidant amount of a compound having the following general formula:

(References on following page) References Cited in the file of this patent UNITED STATES PATENTS Thomas et a1. Mar. 27, 1945 Trautman et a1. IFeb. 25, 1947 Von Fuchs et a1 June 1, 1948 Patterson et a1. Oct. 26, 1948 

1. A MINERAL LUBRICATING OIL CONTAINING AN ANTI-OXIDANT AMOUNT OF A COMPOUND HAVING THE FOLLOWING FORMULA: 